Epicardial heart lead and assembly and method for optimal fixation of same for cardiac pacing

ABSTRACT

An epicardial lead with an insertion assembly for attaching same into good stimulating contact with the heart wall, the lead having movable fixation means for fixing the distal electrode head to the heart wall in combination with a stimulating probe electrode for delivering stimulus signals to the heart. The fixation element is preferably of a corkscrew configuration, oriented normal to the lead axis, and is normally contained within an enclosed electrode chamber. The insertion assembly provides means for releasably holding the electrode head while screwing the fixation member into the epicardial wall. Since the fixation member is free to move with respect to the electrode head, the lead can remain free to be hooked to an external pacer during the fixation step. In operation, a separate stimulus probe is inserted in at various points of the epicardium for testing of threshold and when a good threshold is attained, the lead is then fixed to the heart by screwing the fixation member while maintaining the probe electrode in its desired position.

CROSS REFERENCE TO RELATED APPLICATION

Reference is made to the application for EPICARDIAL HEART LEAD ASSEMBLY,invention of Lee Weiss and Michael J. Dalton, filed concurrentlyherewith.

BACKGROUND OF THE INVENTION

This invention lies in the area of leads for delivering electricalsignals to body organs and, more particularly, epicardial leads for usein cardiac pacing systems and having means for fixation to the heartwall.

In cardiac pacing systems it is known that in a certain proportion ofpatients it is desirable to utilize an epicardial lead, to ensure goodfixation and permanent engagement of the lead to the heart wall. This isthe case primarily because in a certain number of patients proper leadfixation cannot be achieved with endocardial leads, or catheters, and inorder to obtain fixation with a desirable threshold an epicardial typelead is required. A number of epicardial leads are presently availablefor use with pacing systems, the most common forms involving a screwtype element at the distal end of the lead, which element serves both asthe stimulus electrode and as the fixation member. In these prior artarrangements, the fixation member is integrally connected to the lead,and while it may be flexible so as to facilitate engagement with theheart wall, the fixation member generally is not movable relative to thelead itself. This prior art feature places certain constraints upon leaddesign, as well as upon the design of insertion tools used for actuallyfixing the epicardial lead to the patient's heart. Examples of prior artepicardial leads and insertion assemblies include those disclosed inU.S. Pat. Nos. 4,007,745, 3,737,579 and 3,875,947.

There are a number of characteristics of the heretofore availableepicardial leads and systems for inserting same which are considered tobe undesirable and which need improvement. For example, the fixationmeans, which generally is a screw or "cork-screw" type element is fixedto the lead in such a manner that rotation of the corkscrew element intothe heart wall involves rotation of the remainder of the lead itself,necessitating special insertion tools for avoiding placing torque on theremainder of the lead. Additionally, there is no restraint upon theability of the operator to continue to turn the corkscrew element afterit has been fully threaded into the heart wall. It is well known that ifthe corkscrew element is turned after it has been fully extended intothe heart wall there is resulting trauma to the myocardial tissue, andfibrosis. Further, it is unpractical to use a screw type element toprobe for a proper position which gives a desirable threshold, sincerepeated engagement and disengagement of such a corkscrew type elementcauses unwanted if not intolerable trauma to the myocardial tissue. If aseparate probe element is used to determine a position for obtaining agood threshold placement, this is still a very unsatisfactory techniquesince the probe element must be removed and the corkscrew elementinserted. Generally the results are not optimal, both because it isdifficult to reinsert the corkscrew element at the same place as theprobe had been inserted, and because the surface characteristics (andthus the threshold characteristics) of the corkscrew element aredifferent from the probe which had been used.

In other prior art leads, an attempt is made to screw into the hearttissue axially, by somehow applying rotational force from the proximalend of the lead. See, for example, U.S. Pat. Nos. 3,827,428 and3,974,834.

There is thus a substantial need in cardiac pacing systems for a meansand a method for efficient and reliable fixation of an epicardial lead,providing for optimum contact electrode placement and maximum securefixation.

SUMMARY OF THE INVENTION

It is a first object of this invention to provide a lead having aseparate fixation means designed to be operated so as to avoid trauma tothe myocardial tissue at the point of pacing, in combination with aseparate stimulating electrode, the stimulating electrode being designedboth for optimum delivery of stimulating pulses to the heart and forinitial probing to determine a good site for permanent implantation. Itis a second object of this invention to provide a tool assembly forefficient and reliable insertion of a sutureless epicardial electrode.

It is another object of this invention to provide a lead with electrodemeans for probing the heart to determine a good site for stimulatingwith low threshold and then providing good fixation without withdrawingthe probe element which remains as the stimulus electrode.

It is another object of this invention to provide a form of electrodefor a pacing lead, and an accompanying insertion tool assembly forproviding good sutureless placement of an epicardial lead.

It is a further object of this invention to provide means for reliablecoupling and decoupling of a lead to a heart wall or to the wall ofanother body organ, including an insertion tool assembly to be used incombination with the lead which remains fixed in the heart wall.

It is another object of this invention to provide means for achievingoptimal fixation of an epicardial lead by inserting a corkscrew elementa predetermined amount into the heart wall.

It is another object of this invention to provide a method forefficiently probing a patient's heart to determine a position for fixinga stimulating electrode, and for achieving optimal fixation of thestimulating electrode once such good position has been found.

It is another object of this invention to provide a lead with fixationmeans at its distal end, with fixation means are directly manipulable byan insertion tool applied to such distal end.

In accordance with the above and other objectives as are discussedhereinbelow, there is provided an epicardial heart lead having fixationmeans, preferably including a screw type element, which is movablerelative to an electrode chamber at the distal end of the lead, suchthat the fixation means can be attached to the heart wall while theremainder of the lead is free and unaffected by the fixation operation.The fixation element is normally retained within the electrode head by amesh-reinforced membrane. The lead comprises, at its distal end, a probeelement which is connected to act as a stimulating electrode, whichprobe element is mechanically independent of the fixation element butwhich is positioned such that engagement of the heart wall by thefixation element secures the probe electrode at the desired position inthe patient's heart. For operation in conjunction with the lead there isprovided an insertion assembly including means for rotating the fixationelement and means for releasing the lead from the insertion assemblyafter proper fixation has been achieved. The preferred embodimentpreferably also includes means for constraining further movement of thefixation element after it has been fully moved out of its housing andinto the myocardium, so as to minimize trauma and fibrosis resultingfrom the fixation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of the distal electrode head of the lead of thisinvention, illustrating in detail the fixation and probe elements.

FIG. 2 is another side view of the distal electrode head, as seen from aposition longitudinally distal from the end of the lead, furtherillustrating the desired position of the probe element and a portion ofthe mechanism for operating the fixation element.

FIG. 3 is a perspective view of the probe element.

FIG. 4A is a detailed illustration of the insertion tool 60 and screwdriver tool 70 comprising the insertion assembly of this invention.

FIG. 4B is a sketch of the bottom view of the insertion tool 60.

FIG. 5A is a detailed view showing the engagement of the insertion toolassembly with the electrode head at the start of the procedure of fixingthe electrode to the heart wall;

FIG. 5B is a detailed view showing the relation of the insertion toolassembly to the electrode head at the time of complete insertion of thefixation element into the heart wall; and

FIG. 5C is a detailed view showing the relation of the insertion toolassembly to the electrode head after fixation has been completed andafter withdrawal of the screwdriver tool within the insertion tool forrelease of the electrode head.

FIG. 6A is a side view of an alternate embodiment of the insertion tool60.

FIG. 6B is a side view, partially broken away, of a bottom portion 86which is interfitted onto the insertion tool of FIG. 6A.

FIG. 6C is a sketch of a top view of the element 86 of FIG. 6B.

FIG. 6D is a sketch showing bottom element 86 adhered to insertion tool60, with the screwdriver tool 70 in place within insertion tool 60.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, there is shown a view of the electrode headportion of the lead of this invention. The main length of the lead isdesignated as 31, which is a conventional insulating body-compatiblecasing embedding the conductor 34 (for a unipolar embodiment) ofconductors (for a biopolar embodiment) which connect the proximal end(not shown) to the distal electrode. The conductors are suitably helicaland made of a standard conductive material. The proximal end maycomprise any conventional arrangement for connection to the output of acardiac pacer as used in cardiac pacing systems, or to another type ofdevice for other physiological stimulating or sensing systems. The leadcasing is preferably made of a medical silicone.

The lead casing 31 develops, at the distal end, into an enlarged leadportion 32 just proximal of the electrode head 33, both of which areformed of a suitable elastomer. In a preferred embodiment, enlargedportion 32 has a diameter of about 0.09 inch, while electrode head 33has a diameter of about 0.440 inch. Within enlarged portion 32 the coilconductor 34 terminates within crimp sleeve 35, preferably formed oftitanium, and the proximal portion 36 of probe 37 is positioned withinthe end of conductor 34 and in tight conductive relation thereto. As isseen by observation of FIGS. 1, 2 and FIG. 3 as well, probe 37 curvesaround near the perimeter of electrode head 33 and then dropsdownwardly, terminating in needle portion 38 which forms the actualstimulus stip for delivery of stimulus signals which have been generatedin the stimulus pacer. Stimulus portion 38 is suitably a 4 mm length of20 mil wire, pointed at the end as shown, such that it can easilypenetrate or probe into the heart wall. It may also suitably include aball, or sphere 39, as seen in FIG. 3, to modify the stimulus electrodegeometry for the purpose of enhancing the electric field, whereby betterthreshold is obtained. The probe portion 38 is displaced from theproximal portion 36 so as to make it less susceptible to be dislodged ifthe main portion 31 of the lead is moved.

Still referring to FIG. 1 there is shown an inner chamber 48 defined bychamber housing 49, preferably made of titanium. Chamber 48 housesscrews 50 which, in the preferred embodiment, constitutes the fixationmember of the lead of this invention. Screw 50 is suitably made of MP35N alloy, providing spring steel characteristics. Screw 50 is attachedat its top to an electrode cap 54 which penetrates upward through thetop surface of electrode lead head 33. Cap 54 fits loosely through thesurface of head 33, such that it can be rotated by application of ascrewdriver type tool to the slot 55 in cap 54, which slot isillustrated in FIG. 2. Before use, screw 50 is contained at the bottomby a membrane 52 which is secured to the bottom surface of head 33 by asuitable medical adhesive. Membrane 52 is suitably made of siliconereinforced with Dacron (Registered Trademark). It is of sufficientstrength to prevent screw element 50 from falling through it, but iseasily penetrated by the tip of screw element 50 when it is rotated.While element 50 can be screwed down and through membrane 52, the meshwithin it acts to prevent further rotation of the screw element after ithas advanced out of chamber 48. A Dacron (Registered Trademark) mesh 53is suitably adhered to the bottom of membrane 52, as illustrated.Additionally, the bottom surface of electrode head 33 may be formed witha curvilinear surface which is slightly concave upward, for more optimalinterfacing with the heart wall.

It is to be noted however that an important structural feature of thedistal end of the lead is that the fixation member 50 is free to rotateand move with respect to the electrode head 33. Other than the membrane52 which is specifically designed to be penetrated by the screw member50, there is no constraint to movement of the screw member 50 within thechamber 48. Electrode cap 54 has a base plate which prevents movement ofthe screw element 50 out of the chamber 48 in either the upward ordownward direction. Movement of member 50 is in a plane transverse tothe axis of the lead, i.e., substantially at right angles to the leadaxis. Torque can be applied directly to member 50 through rotation ofcap 54.

It is seen that needle probe 38 has a fixed geometrical relationship tothe axis along which screw element 50 is moved. In operation, thephysician who is implanting the pacer and connecting the lead to theheart wall probes with needle probe 38, testing patient threshold, untila desired stimulating location is found. At this time, the physicianretains the needle 38 fully inserted into and engaging the heart wall atthe desired location, and then moves fixation element 50 so as tosecurely engage the electrode head so as to maintain probe 38 in secureposition at the point where the physician wants it. Note that element 50and electrode cap 54 move freely relative to the electrode head 33, andat a right angle to the lead axis. By this means, the step of fixation,during which element 50 is actually screwed into the heart wall, doesnot affect at all the maintenance of probe 38 at the desired location.Note that the force being exerted does not tend to displace probe 38.Probe 38, being of a basically needle-like geometry, can be inserted atvarious points in order to find the desired threshold position, withoutcausing any great amount of trauma to the heart wall. Also, its designis better adapted than a screw type configuration for avoiding growth oftissue around the stimulus such as reduces chronic thresholdundesirably. Since the stimulating probe 38 is physically separate fromthe implanted screw element 50, any tissue that grows in around screwelement 50 has no effect on the stimulus characteristics of the probeitself.

Referring now to FIGS. 4A and 4B, there are shown views of the insertiontool 60 and screwdriver tool 70 which, in combination, comprise theinsertion tool assembly of this invention. Insertion tool 60 isgenerally cylindrical tube made of a suitable plastic material, havingan upper portion 61U of a given inner diameter and a bottom portion 62Lof a larger inner diameter relative to the upper portion. As noted atpoint 62, the wall thickness changes between upper portion 61U and lowerportion 62L, thereby providing the change in inner diameters of the twoportions. The inner diameter of portion 62L is, in the preferredembodiment, 0.436 inch, which is to be compared with the 0.440 outsidediameter of the lead head. The small bottom chamber defined by walls 62Land horizontal stop elements 63 is thus of a size and form to frictioncapture electrode head 33. The opening 64 defined by stop elements 63has a diameter which is slightly larger than the diameter of electrodecap 54, so that the cap can freely extend through the opening. Note thatthe stop elements hold cap 54 in axial alignment as it is being rotated,thus insuring proper entry of screw element 50 into the heart wall. Asseen in both FIG. 4A and FIG. 4B, there is a notch 65 at the bottom ofinsertion tool 60, having a radius of about 0.08 inch, providingsufficient opening to accommodate enlarged lead portion 32 when theelectrode head is captured by the tool 60. By this means, the mainlength of the lead remains outside of the tool, and is free thereof.Further, this outside length is unaffected by the fixation step. Notch65 also can be used to guide the tool back onto the electrode head ifthere is need to affix the tool to the electrode a second time.

The screwdriver type tool 70 is comprised of an upper portion 71 of afirst larger diameter, and a lower portion 72 of a smaller diameter. Asis seen by referenced FIGS. 5A, 5B and 5C, the screwdriver tool ispositioned within the insertion tool 70, the diameter of lower portion72 being smaller than the inner diameter of portion 61U of the insertiontool. Screwdriver tool 70 is forced into the insertion tool by expandingthe insertion tool at slit 67. Slit 67 is shown, in FIG. 4B, as beingapproximately 0.09 inch in width, but may be less, the purpose beingonly to allow the tool to be expanded sufficiently to fit thescrewdriver tool inside of it. In any event, slit 67 is sufficientlysmall so that the casing 31 of the lead cannot get into it. Further, thepresence of screwdriver tool 70 inside of tool 60 leaves insufficientroom for putting the lead within tool 60.

Screwdriver tool 70 has at the bottom extension thereof an enlarged ringportion 74, of an outer diameter which is greater than the innerdiameter of portion 61U but less than the inner diameter of portion 62Lof the insertion tool. Thus, screwdriver tool 70 is normally maintainedwithin insertion tool 60 at a position such that enlarged ring 74 isfound between the stops 63 and the thickness change point 62. Extendingfrom the very bottom end of screwdriver tool 70 is a screwdriver blade75, adapted to interfit with the screwdriver receiving slot 55 ofelectrode cap 54. Although blade, or bit 75 is illustrated as aconventional screwdriver type blade, it may have an Allen-type form foreasier insertion of the bit into the slot or comparable receivingreceptacle 55 of electrode cap 54. Other mating forms for achievinginteraction of tools 60 and 70 may also be used.

An additional feature illustrated in FIGS. 4A and 5A comprises means forrestraining movement of the corkscrew element 50 once it has been fullyextended down and out of the bottom of distal electrode chamber 48. Thismeans is provided by the teeth 68 at the top of insertion tool 60 andthe teeth 73 around the perimeter of screwdriver tool 70 between upperportion 71 and lower portion 72. Tool 70 is made of a predeterminedlength relative to tool 60, such that when the screwdriver bit 75 restswithin slot 55 of electrode cap 54, teeth 73 are above matching teeth 68by a distance comparable to the axial or longitudinal length ofcorkscrew element 50. As the screwdriver is rotated by the physician toscrew element 50 into the heart wall, teeth 73 advance relatively towardteeth 68. When the corkscrew element 50 is fully inserted, the teeth 73engage with teeth 68, preventing further rotation of screwdriver tool70. By this means, the operator or physician is prevented fromcontinuing to rotate the screw 50 after it has been fully moved out ofchamber 48 and into the myocardium (designated as H). This preventsunneeded and unwanted rotation of element 50 such as would tear theheart wall and produce trauma and resulting fibrosis.

Referring now to FIGS. 5A-5C, there are shown three diagrammaticillustrations off the manner of fixing the screw element 50 into theheart H, and of then releasing the fixed electrode head 33 from the toolassembly 60, 70. In FIG. 5A, the screwdriver tool has been positioned sothat it is engaging the electrode cap 54, but the corkscrew element 50has not yet been moved through the membrane 52 and into the heart H.Note that the distal electrode head 33 is snugly friction capturedwithin the bottom of tool 60, with the electrode cap 54 extending abovestop elements 63, so that the receiving slot 55 is available to receivethe screwdriver blade 75. The enlarged ring portion 74 of thescrewdriver tool is within the larger inner space defined by wall 62L.As the screwdriver element is rotated, the cap 54 and the screw element50 carried thereby are caused to rotate outward and downward fromelectrode head 33, thereby engaging the heart H. When the screw element50 is fully extended out of head 33, the enlarged ring portion 74 abutsstops 63, and gear teeth 73 engage gear teeth 68. This is the conditionillustrated in FIG. 5B. At this point, fixation has been achieved, andit is desired to release the electrode, leaving it securely in placeattached to the heart wall. This is done by pulling up on screwdrivertool 72, so that its blade disengages from slot 55 in cap 54. At thesame time, as seen in FIG. 5C, outer ring 74 comes into contact with theinsertion tool wall at point 62, forcing that wall radially outward,thereby releasing electrode head 33 from its friction fit within lowerwall 62L. Under these circumstances, the physician simply withdraws theinsertion assembly from the electrode head, leaving the electrode firmlyin position.

Referring now to FIGS. 6A-6D, there is illustrated an alternateembodiment of the insertion tool assembly of this invention whichpossesses certain additional advantages. As seen particularly in FIG.6A, the insertion tool 60 has a slit 67 which is very narrow, suitably0.015 inch. Further, it extends from the bottom longitudinally up toonly about the midway point or less of the insertion tool, where itterminates in hole 85 which is designed to relieve stress. By notextending the slit the entire length of tool 60, it is more rigid at thetop part and thus can be handled somewhat more effectively. Also, it isseen that the sloped portion 62 is contiguous with a longitudinallystraight portion 82 which terminates in a shoulder 83, which shoulder isdesigned to block the ring portion 74 of the screwdriver tool so that itcannot be pulled out of tool 60. In practice, the inner diameter R₁within walls 62L is suitably 0.435 inch; the diameter R₂ is 0.410 inch,and R₃ is 0.385 inch. By constructing the ring portion 74 of thescrewdriver tool to be 0.425 inch in diameter, it is seen that when thescrewdriver tool is pulled up to the point where ring portion 72corresponds to radius R2, the lower walls 62L are expanded to releasethe electrode head. However, ring portion 72 cannot be pulled beyond theshoulders 83.

Referring to FIGS. 6A-6C, it is seen that the bottom portion of tool 60which captures the electrode head is a separate piece 86, having upperannular portion 87 with a slightly larger inner diameter than R₁.Portion 87 is designed to interfit with notch 84 as in FIG. 6A. Asomewhat enlarged notch 88 is illustrated, to provide more room forfeeding the lead portion 32 outside of the insertion tool.

In practice, the insertion assembly of the embodiment illustrated inFIGS. 6A-6D is fabricated by first drawing the screwdriver tool 70 upthrough the bottom opening of tool portion 60, until ring portion 74 isfully within portion 60. Then the bottom portion 86 is fitted into notch84 and secured with a suitable adhesive, resulting in the assembledcombination of insertion tool 60 and screwdriver tool 70, as illustratedin FIG. 6D.

There is thus shown apparatus and a method for probing the heart wall todetermine a good place for obtaining optimum threshold stimulation ofthe heart (using conventional threshold testing means) and fixating thestimulating probe in the heart while maintaining the desired probeposition, such fixating being implemented without placing any stress ortorque on the remaining part of the lead. The fixation mechanismutilized is different and independent from the pacing and probingelectrode, which electrode can be designed with a geometry which neednot take into account any fixation requirements. The insertion apparatusutilized provides for easy and secure clamping of the electrode head forprobing and fixating, and equally efficient and easy releasing of theelectrode head when it has been secured to the heart wall.

Accordingly, the objects as outlined above are achieved efficiently andreliably. In the preferred design, the physician turns the distal end ofthe electrode 21/2 turns to achieve fixation, after which furtherrotation is prevented. Optimal fixation is achieved because thephysician knows that he must continue to rotate the fixation elementuntil it can no longer turn. If he turns it less, it is not extendedfully for optimal fixation. While the stop mechanism has beenillustrated as being incorporated into the insertion tools, it canequally be designed into the head itself by putting the two sets ofteeth on the bottom of cap 54 and the bottom of chamber housing 49respectively.

While the preferred lead as illustrated comprises a separate probe 38and fixation element 50, it is to be understood that fixation member 50might also be utilized as a stimulus electrode, either alone or incombination with a probe element. Electrical connection may be madebetween conductor 34 and fixation member 50 by conventional commutatingmeans.

I claim:
 1. A lead for delivering signals from a signal source such as acardiac pacer to a body organ such as a patient's heart, the lead havinga proximal end adapted to connect to the signal source, a flexibleconductor length adapted for connecting signals from the proximal end toa distal end, and a distal electrode end adapted for delivering thesignals and for being fixed to an organ such as the patient's heart, thedistal electrode end being characterized by comprising the followingimprovements:movable fixation means normally mounted within said distalend for attaching to the wall of the body organ, said fixation meansbeing rotatable within and out of said distal end at an anglesubstantially normal to the axis of said conductor length and having areceiving portion adapted to extend through said end, said receivingportion having means for receiving a rotating tool outside of said endfor rotating said fixation means along an axis substantially normal tosaid conductor length; and stimulating electrode means connected to saidconductor length and rigidly fixed relative to said distal end forinsertion into the organ wall for delivering the stimulation signals. 2.The lead as described in claim 1, wherein said stimulating means isadapted to be a probe element.
 3. The lead as described in claim 1,wherein said probe element is needle shaped.
 4. The lead as described inclaim 1, wherein said movable fixation means comprises a corkscrewelement.
 5. The lead as described in claim 4, comprising means forlimiting the extent of movement of said corkscrew element duringinsertion thereof into the organ wall.
 6. The lead as described in claim4, comprising a diaphragm element for normally retaining said corkscrewelement fixed within said distal lead end.
 7. The lead as described inclaim 1 wherein said stimulating electrode means comprises a surfaceportion which is substantially ball shaped.
 8. The lead as described inclaim 1, wherein said distal end has a chamber and said movable fixationmeans is housed in said chamber, said distal end containing a membraneforming a lower side of said chamber, said membrane being penetrable bysaid fixation means.
 9. The lead as described in claim 8, wherein saidmembrane is mesh-reinforced.
 10. The lead as described in claim 8,wherein said fixation means comprises a corkscrew element, incombination with an insertion assembly for rotating said corkscrewelement, in combination with an insertion assembly for rotating saidcorkscrew element, said insertion assembly having means for holding saidcorkscrew element in alignment while it is rotated.
 11. A lead fordelivering signals from a signal source such as cardiac pacer to a bodyorgan such as a patient's heart, the lead having a proximal end adaptedto connect to the signal source, a flexible conductor length adapted forconnecting signals from the proximal end to a distal end, and a distalelectrode end integrally connected to said conductor length and adaptedfor delivering the signals to the body organ, the distal electrode endbeing characterized by comprising a chamber and rotatable fixation meansmounted therein for engaging the wall of the body organ, said fixationmeans having means for limiting rotation to an axis substantially normalto said conductor length at the point where it is connected to saiddistal electrode end, said fixation means having a first engagingportion for engaging said patient's heart and a second portion normallyextending out of said distal end for receiving a tool for impartingrotation to said fixation means.
 12. The lead as described in claim 11,wherein said lead comprises a stimulating electrode mounted in fixedposition on said distal electrode end and electrically connected to saidflexible length.
 13. The lead as described in claim 11, wherein saidfixation means comprises a corkscrew element with an axis of rotationsubstantially normal to the axis of said lead length.
 14. The lead asdescribed in claim 13, wherein said distal electrode end comprises achamber for housing said corkscrew element, said chamber beingconfigured to restrain the movement of said corkscrew elementsubstantially along said axis of rotation.